The present invention relates to a safety switch for monitoring an adjacent position of two parts that are moveable relative to each other, and more particularly, the invention relates to a safety switch for monitoring a closed position of a guard door in an automated installation.
Safety considerations relating to protection against accidents are playing an increasingly major role in the planning and design of automated installations. Various protective measures are used to make the installations safe, such as emergency-off switches, light barriers and what is known as guard doors, which prevent access to a dangerous part of the installation in conjunction with guard fences. The opening of the guard door has to be detected in a fail-safe manner during operation of the installation, since the open guard door represents a safety risk. The relevant European Standard EN 954-1 and related or comparable regulations (for example the new IEC EN 61508 or prEN ISO 13849-1 which is derived from the latter) stipulate the requirements for the protective measures. The present invention relates to safety switches which are intended and designed for these safety related applications, and thus the safety switches satisfy at least Category 3 of EN 954-1, or comparable safety requirements.
There are various approaches for implementing safety switches in order to monitor the closed position of a guard door, and more generally the closed position of two parts moveable relative to one another, with a sufficient degree of fail-safety. In addition to mechanical switches, which can also provide an interlocking function, there are various types of non-contact safety switches. These offer advantages in dirty environments. The actuator and sensor In one known type of non-contacting safety switches, the actuator and sensor are magnetically coupled to one another in the closed position. In order to prevent manipulation, coded magnet arrangements are used in some cases.
In another type of non-contacting safety switch, individually coded communication is used between the sensor and the actuator, with this communication being possible only when the moving parts are in the closed or adjacent position. For safety switches of this kind, so-called transponders (in some cases also referred to as “tags”) are particularly used. The transponders transmit an individual coding to the sensor when they are transformer-coupled to that sensor. A safety switch of this kind is marketed by the company Eucher GmbH & Co. KG, 70771 Leinfelden-Echterdingen, Germany, under the product name CES.
Another prior art safety switch is offered by the company K. A. Schmersal GmbH, 42232 Wuppertal, Germany, under the product name BZ 16. This prior art safety switch suffers from the disadvantage that a dedicated switch variant has to be used for each direction of approach, i.e. the direction of approach from the actuator to the sensor. By way of example, if a safety switch is required for an application in which the actuator is intended to be moved toward the sensor from above rather than from the front, a different variant of the known safety switch is required. This not only makes it more difficult to install the safety switch but also leads to increased storage costs, both for the manufacturer and for the user, since it is desirable to always have a certain number of spare parts of important components available for smooth production.
In the case of the CES safety switch from Euchner, it is possible to mount the “sensor head” (i.e. that part of the sensor which contains the sensor antenna) in different orientations on the safety switch in order to avoid this problem. Different approach directions can thus be achieved by tilting the sensor head. This solution allows reduced storage, but results in a complicated installation.